Embodiments relate generally to heat exchanger coils and, more particularly, to a method and apparatus for expanding and belling heat exchanger coils having aluminum or copper tubes.
Plate-fin type heat exchangers are commonly employed in air conditioning and refrigeration systems. A plate-fin heat exchanger coil is commonly constructed with a plurality of flat, parallel plates having laterally spaced holes for receiving refrigerant tubes, or hairpin tubes therein. At each end of the plate-fin bundle, there is a tube sheet composed of heavier material, and adjacent one of the tube sheets, the open ends of the hairpin tubes are fluidly connected with a U-shaped return bend secured thereto by way of soldering, brazing, or the like. When the coils are installed into a refrigeration system, the refrigerant flows through the hairpin tubes, and the air to be cooled or heated passes over the plate-fins, causing heat transfer to occur.
Though compression expansion is a commonly used when manufacturing heat exchanger coils, such a process has known complications. The conventional compression expansion process generally includes passing tube expanding rods through the open ends of the hairpin tubes and then belling the tube. A backing plate is placed against the tube bends to prevent the tubes from being driven out of the unit as the expanding tools are forced therethrough. As a result of this holding action, the tubes are compressed rearwardly as they are expanded outwardly by the tools. This, in turn, causes the tubes to shrink so that the axial length of each tube can vary dramatically. Because of the differences in tube length, belling of the tubes is difficult and generally results in uneven or misaligned bells being formed in the tube ends. The bell ends can also be uneven, which makes automatic brazing or soldering difficult.